Some conventional user interface elements allow users to select an item from among several listed items. Such user interface elements can include a list box, combo box and/or drop down menu. Other user interface elements allow users to select an item from an ordered hierarchy of items.
A tree view user interface element contains an item at a first level of the hierarchy that is expandable to display the items at a second level of the hierarchy, where the displayed items are children of the first item. Items in the second level, and subsequent levels, of the hierarchy may be expandable as well. The tree view user interface element can require significant vertical screen space to concurrently display multiple items at each level of the hierarchy.
An expandable menu (e.g., a popup menu or a drop down menu from a menu bar) can also allow selection of items in a hierarchy of items. On selecting a first level item from a menu of items (e.g., by positing an on-screen cursor), a second sub-menu appears (e.g., a cascading menu or fly-out) with child items of the next level of the hierarchy. Expandable menus require both significant vertical and horizontal screen space as each sub-menu level cascades from the previous selection.